The invention relates to a seal ring for sealing about a relatively-rotatable shaft and, more particularly, such a seal ring having lubricant pockets and a process of making it.
A known seal ring has a supporting ring to be held about a relatively-rotatable shaft. An elastic ring is fixed at one, lipped edge to the supporting ring in a leak-proof, non-rotating manner, initially to project radially inward therefrom, and then to bend to engage the shaft resiliently and substantially axially with a sealing surface adjacent the other, free edge of the elastic ring. The sealing surface is interrupted at the other, free edge of the elastic ring which, in use, faces a lubricant-containing space that is to be sealed by lubricant pockets.
The lubricant pockets open from the sealing surface only in the direction of the other, free edge of the elastic ring to maintain the sealing function of the sealing surface. In the position of use described, when the sealing surface is substantially axial of the shaft, the lubricant pockets are defined radially by circumferential, bottom surfaces and circumferentially by baffle, side surfaces at least one of which is at an obtuse, included angle in the lipped, elastic ring to the adjacent sealing surface of the lipped, elastic ring and an acute angle to the axis of the ring to be at acute angles to the surface of the shaft and to its rotational axis.
Published European patent application No. 33 963 discloses a seal ring of the type described above. The bottom surfaces of its lubricant pockets have an unvarying distance from the shaft and are delimited from the baffle surfaces of the lubricating pockets by sharp edges. The baffle surfaces are in the form of ribs extending parallel to one another at the same angle to the surface of the shaft in all areas. The hydrodynamic effectiveness of the baffle surfaces is, therefore, dependent on the sealed shaft's turning in a certain direction at a very specific rotary speed. Departures therefrom, consequently, always impair of the sealing action of the seal ring, by increased wear and/or increased leakage, for example.
The lipped, elastic ring having the lubricant pockets can be made by pressing or injection-molding processes. In some cases, it is possible to join it to the supporting ring simultaneously, but this may be uneconomic.
German Federal Patent publication No. 32 46 152 describes another known process for making such a seal ring. In it, a tubular sleeve is cut from a previously-produced and fully-vulcanized tube for use as the lipped, elastic ring. For producing a flange-like supporting ring on the lipped edge of the elastic ring, the lipped edge is pushed onto a mandrel of continuously increasing diameter. Fixing the flange or supporting ring thereto can then be done very quickly in the course of a process that can be substantially automated. Difficulties are then encountered, however, in the creation of hydrodynamically-acting pump-back elements on the sealing surface of the lipped elastic ring.
It is known to produce such hydrodynamically-acting pump-back elements by grinding or pressing recesses into the sealing surface of the elastic ring. These operations involve mechanically working the sealing surface, however, and this is not only extremely expensive, but also problematical because even the slightest differences in the shape or form of the individual pump-back elements will result in decidely different hydrodynamic action and, usually, poorer sealing.